The present invention relates to a heat development apparatus which heats a heat-developable photosensitive material or photosensitive heat-sensitive recording material (heat-developable sheet) having an latent image by an exposure formed therein while being conveyed so that it is developed.
In the art of plate-making image forming apparatus for making a printing plate or image forming apparatus for recording medical images such as CT (computed tomography) and MR (magnetic resonance), an image forming apparatus employing a dry system which performs wet process-free heat development to form an image has been noted. Such an image forming apparatus employs a photosensitive and/or heat-sensitive recording material (photosensitive heat-sensitive recording material) or a film made of heat-developable photosensitive material (hereinafter referred to as xe2x80x9cheat-developable sheetxe2x80x9d). In its exposure section, the heat-developable sheet is irradiated (scanned) with a laser beam to form a latent image therein. Thereafter, in its heat development section, the heat-developable sheet is brought into contact with a heating means to cause heat development thereof. Subsequently, the heat-developable sheet which has been heated in the heat development section is cooled to form an image thereon. The heat-developable sheet is then discharged out of the apparatus. Such a dry system image forming apparatus (hereinafter referred to as xe2x80x9cheat development apparatusxe2x80x9d) can not only form an image in a short period of time as compared with the wet process but also eliminate the problem of disposal of waste liquid as seen in the wet process and thus can be much expected to be in growing demand in the future.
Such a heat development apparatus has heretofore employed a process which comprises pressing the heat-developable sheet against the heating means to facilitate development. In particular, a heat development system comprising a heating means made of heat plate and a plurality of hold-down rollers which are disposed opposed to each other between which the heat-developable sheet is conveyed is desirable because it is excellent in uniformity of heating and exhibits a strong resistance to contamination by dust or other foreign matters, making it possible to drastically eliminate uneven development, which is a problem of the conventional system.
Although in the foregoing conventional heat development apparatus, as the apparatus power supply is switched on to actuate the apparatus, the temperature of the heat plate gradually rises to a predetermined value, the hold-down roller which is disposed in contact with the heat plate to receive heat transmitted from the heat plate cannot reach the predetermined temperature at this point. When development is attempted under these circumstances, the heat of the heat plate for heating the heat-developable sheet is taken out by the hold-down roller through the heat-developable sheet, resulting in the heat development at a low temperature that can leave the heat-developable sheet undeveloped. Therefore, the heat development apparatus is forced to wait further until the hold-down roller is warmed to a predetermined temperature and thus is ready to start development. Thus, the heat development apparatus needs a prolonged rising time. For example, it takes from about 17 to 18 minutes for the heat plate to reach the predetermined temperature while it normally takes about 30 minutes for the hold-down roller to be warmed to the predetermined temperature and ready to start development.
In the conventional heat development apparatus, when continuous heat development is effected, heat transmitted from the heat plate is taken out or shielded by a continuous flow of the heat-developable sheets to lower the temperature of the hold-down roller. Therefore, the subsequent heat development of heat-developable sheet must be effected at a predetermined interval of time during which the temperature of the hold-down roller is restored, making it difficult to enhance the development capacity.
There has been proposed an approach involving the correction of exposure on the basis of estimation of drop of roller temperature. However, this approach is disadvantageous in that correction of exposure can be hardly made, resulting in unstable heat development.
The present invention has been worked out in the light of the foregoing circumstances. An object of the invention is to provide a heat development apparatus which can be actuated in a reduced rising time and perform continuous heat development of heat-developable sheet under a stabilized temperature gradient.
In order to accomplish the foregoing object of the invention, the heat development apparatus according to a first aspect of the invention is a heat development apparatus which heats a heat-developable sheet having a latent image formed therein by an exposure while being conveyed therethrough so that it is developed, comprising a heating means for heating the heat-developable sheet, a hold-down roller disposed opposed to the heating means for pressing the heat-developable sheet against the heating means; and a temperature adjusting means for raising the temperature of the hold-down roller to a predetermined value.
In this heat development apparatus, as the apparatus power supply is switched on, the hold-down roller is directly warmed by the temperature adjusting means. Accordingly, unlike the conventional arrangement in which the hold-down roller is indirectly warmed by heat conduction of the heating means, the temperature of the hold-down roller reaches a predetermined value that does not impede development at almost the same time as the heating means. As a result, the waiting period required until the hold-down roller is further warmed after the temperature of the heating means has reached a predetermined value as in the conventional case can be omitted, making it possible to reduce the rising time of the apparatus.
The heat development apparatus according to a second aspect of the invention is characterized in that the temperature adjusting means generates radiation heat to warm the hold-down roller.
In this heat development apparatus, the temperature adjusting means generates radiation heat to warm the hold-down roller, and the temperature of the hold-down roller thus warmed is controlled to have no effect on the development of the heat-developable sheet. In this manner, heat development cannot be conducted in an unstable manner. Thus, heat development can be always conducted in a stable manner.
The heat development apparatus according to a third aspect of the invention is characterized in that the temperature adjusting means warms the hold-down roller in such a manner that the temperature gradient between the heating means and the hold-down roller is kept constant.
The heat development apparatus is arranged such that the temperature of the hold-down roller which has been warmed is kept almost equal to or slightly lower than that of the heating means to keep the temperature gradient between the hold-down roller and the heating means constant. In this arrangement, continuous heat development process can be effected without having the heat of the heating means to be taken out by the hold-down roller through the heat-developable sheet. Accordingly, heat development can be effected in an invariably stable manner, making it possible to enhance the processing capacity.
The heat development apparatus according to a fourth aspect of the invention is characterized in that the hold-down roller comprises a temperature adjusting means incorporated integrally therewith.
In the foregoing heat development apparatus, the hold-down roller is of self-heating type comprising a heater provided in the interior of a hollow cylindrical core metal so that a temperature adjusting means is incorporated integrally therewith. In this arrangement, the space that would be required if the temperature adjusting means is disposed in the vicinity of the hold-down roller can be omitted to reduce the size of the apparatus. Further, since the various hold-down rollers can be separately temperature-controlled, uniform development conditions can be provided all over the length of the heat development section, e.g., by predetermining the temperature of the hold-down roller disposed at the inlet of the heat development section, where the temperature drop is highest due to the entrance of the heat-developable sheet, slightly higher than the standard value, predetermining the temperature of the hold-down roller disposed at the outlet of the heat development section, where the temperature drop is the lowest, slightly lower than the standard value, and forming a temperature gradient such that the temperature of the rollers gradually decreases from the inlet toward the outlet.
The heat development apparatus according to a fifth aspect of the invention is characterized in that the hold-down roller is temperature-controlled with a temperature sensor provided on the outer surface thereof.
In the foregoing heat development apparatus, the various hold-down rollers can be individually temperature-controlled with a temperature sensor to enable precision temperature control.